1. Technical Field
This invention relates to a housing for an electric device which comprises one or more electric components, such as a transformer or an X-ray tube and related components and which is filled with an insulating and/or cooling liquid, like mineral oil or a synthetic liquid. Such insulating and cooling liquids, and particularly oil, have the property of aging with time and temperature, especially if exposed to air which causes a sludge formation. If protected from air the formation of sludge is very effectively retarded at all temperatures. During operation of such an electric device, heat develops in the electric component or components and the liquid changes its volume because of its thermal expansion. Therefore, the housing should be on the one hand hermetically sealed and on the other hand constructed in a way that the liquid can easily expand.
2. Description of the Prior Art
From Swiss Patent CH-436,468 it has been known to put on top of an oil filled housing for a transformer an open expansion vessel which comprises a membrane separating the oil from open air in a hermetically sealed manner. This membrane consists of a combination of a metal foil and at least one layer made out of synthetic resin. When the oil expands and contracts, then the membrane extends upwardly and downwardly, respectively.
German Patent DE-3,206,368 also discloses a housing for a transformer and an extension vessel for the insulating and cooling liquid. The extension vessel comprises a membrane having the shape of a bag which floats on the surface of the oil and has an interior which is connected to the outer air.
Finally, German Patent DE-3,240,724 shows a housing for a transformer and a switching unit. The transformer is immersed in an insulating and cooling liquid and the switching unit which is surrounded by an insulating gas. In order to separate the liquid from the gas, a membrane is located between the oil and the gas. The membrane consists either of one flexible piece or of a combination of flexible pieces and rigid portions. Since this known housing consists of two parts which are separated by the membrane, many parts are necessary to build the housing and thus the production costs of the housing are high.